Variable Frequency function generator ( HELP )

In my college we were asked to make a variable frequency function generator that make ( sine , square , sawtooth ) waves ,
i know that if i had a sine wave i can convert it using a zero detecting circuit with an op-amp to a square wave then using an op-amp as an integrator i can change it into a sawtooth wave BUT my main problem is to build a simple sine wave oscillator with variable frequency ,
i tried many oscillators ; wein bridge , colpitt , crystal and yet i cant find anything that works , if anyone can help please ??

A Wien bridge oscillator works perfectly and is very simple. Post your schematic so we can show you what was wrong.
Colpitts or crystal oscillators are also simple but are used for radio frequencies. Opamps do not work at radio frequencies.

i have deleted most of my schematics as they arent working
and about Wien bridge oscillator , i have read that its hard to make a variable frequency with it because every component should be calibrated separetly in order to work properly , and personally i would prefer using a crystal oscillator and varying the frequency of the output using a varactor or something , i have read about it but i cant get it to work on my simulator , tried Multisim and Proteus and yet , not working ...

If you're wanting a variable frequency generator, you certainly don't want to use (a) crystal(s); as you'd only be able to adjust the frequency a few parts per million. Crystals are used when you want the frequency range to be very narrow, as in a system clock.